Structural isomers of carene persuade apoptotic cell death by inhibiting cell cycle in breast cancer cells: An in silico and in vitro approach

For the first time, our study provides a comprehensive examination of the anti-cancer effects of structural isomers of carene in breast cancer cells, specifically focusing on cell cycle inhibition and the induction of apoptosis. We utilized the hydro-distillation method to extract Piper nigrum seed essential oil (PNS-EO) and identified its bioactive components through gas chromatography-mass spectrometry (GC-MS) analysis. A total of 46 bioactive compounds were isolated via hydro-distillation, identified through GC-MS analysis, and validated by co-injection using GC analysis. The major constituent, 3-carene displayed the most substantial anti-proliferative effect on the breast cancer cell line MCF-7, with an IC₅₀ value of 11.19 µg/mL. Further, docking studies were conducted to evaluate the putative role of 3-carene in inhibiting the cell cycle proteins (CDKN2A, CCND1, CDK4), as well as proteins in the apoptosis pathway (BCL-XL, BAX, BAK, Caspase 3). Additionally, we employed fluorescence-activated cell sorting (FACS) and clonogenic assays to evaluate cell cycle inhibition and time-dependent initiation of apoptosis. Moreover, fluorescence techniques including Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), Hoechst staining, and Propidium iodide (PI) staining were performed to assess cell death and apoptosis. Furthermore, molecular techniques such as quantitative real-time PCR (qPCR) and western blotting were utilized to investigate the mechanism of cell death was elucidated through the inhibition of Bcl-2, MMP2, MMP9, and Akt expression, alongside the activation of Bax, cytochrome C, and Caspases 3 and 9. Our findings indicate that 3-carene, isolated through hydro-distillation, effectively hinders the cell cycle and promotes apoptosis in MCF-7 cells. Consequently, it shows promise for incorporation into combinational anti-cancer therapies, warranting further research.